TECTONIC GEOMORPHOLOGY AND QUATERNARY SLIP RATE OF THE XITIESHAN SECTION OF THE NORTHERN MARGIN FAULT OF QAIDAM BASIN

doi:10.3969/j.issn.0253-4967.2020.06.008

Abstract

Abstract: The northern margin fault of Qaidam Basin(NMFQB)dominates the deformation of the northeastern part of the Qaidam Basin. The study on the Quaternary slip characteristics of NMFQB is of great significance to understand the regional strain-partitioning pattern for the south Qilian orogenic belt, and the extrusion process in the Qaidam Basin. In this paper, Quaternary activities of the fault are discussed based on the remote sensing interpretation, geological survey, trench excavation, GPS topographic profile measurement and OSL dating. The results show that the NMFQB has obvious linear characteristics from the remote sensing image of Xitieshan section. A series of geomorphic traces, such as fault scarps, fault facets, water system displacement, show that the Xitieshan section of the NMFQB is a Holocene active strike-slip fault with minor thrust. Four-stage alluvial fans were identified in the Xitieshan area. The DEM map shows a maximum horizontal displacement of 150m, 38m and 6.5m in the alluvial fan Fan3, Fan2 and Fan1, respectively. The geological age of Fan3 landform in the area obtained by OSL dating is(34.3±3.3)ka, the geological age of Fan2 landform is(11.6±1.0)ka, and that of Fan1 landform is(3.2±0.3)ka. Comparing with the analysis and collation results on the alluvial fans in the northern Qaidam Basin obtained by other researchers, the geological age of Fan3 alluvial fan in the northern Qaidam Basin is about 40ka, that of Fan2 is about 12ka, and the geological age of Fan1 is about 3.5ka. The age of the alluvial fan in the Xitieshan area is basically consistent with the development time of the alluvial fan in the region, indicating that the northern region of the Qaidam Basin was under a large-scale regional uplift during the same period, and the uplift activity was synchronous and recurrent.
Through GPS measurement of fault scarps across faults, the average height of the scarps formed in Fan1 is 1.2m. According to the geological dating of Fan1, the vertical movement rate is calculated to be 0.33~0.38mm/a. The average height of the scarps formed by the alluvial Fan2 is 2.35m. According to the geological dating of Fan2, the vertical movement rate is calculated to be 0.17~0.23mm/a.
We analyze the vertical displacement and related geomorphological ages of the two periods of alluvial fans at the two sites with one west to Xitieshan Town and one east to Quanjihe after measuring the horizontal and vertical displacement data of the geomorphic surface in this area. The Late Pleistocene strike-slip rate of this section is 3.55~4.72mm/a since 40ka and 2.68~3.65mm/a since 12ka, the Holocene strike-slip rate is 1.81~2.1mm/a since 3.2ka, and the Holocene vertical slip rate is 0.33~0.38mm/a. This amount of geological slip rate is consistent with the slip rate of 2~4mm/a from GPS observation.
According to the reverse “S” type structural system, natural profiles and trenching profiles of the northern margin fault of Qaidam Basin, it is believed that the fault was squeezed and uplifted by the Qilian Mountains block in the early stage, and the fault activity was mainly thrust, and in the latter stage, due to the impact of the Altun Tagh Fault, the fault activity takes the form of strike-slip. Controlled by the Altun Tagh Fault, North Qaidam Fault, the Elashan Mountain Fault and East Kunlun Fault, the Qaidam Basin behaves as a block rotating clockwise.

Key words: the northern margin fault of Qaidam Basin, Xitieshan Mountain, sinistral strike-slip, strike-slip fault, thrust fault, activity rate

摘要： 柴达木盆地北缘断裂是控制柴达木盆地东北部的边界活动断裂, 对其晚第四纪的活动性进行研究对于理解南祁连山地区的应变分配模式以及该地区断裂向柴达木盆地内部的挤压扩展过程具有重要意义。文中通过遥感解译、地质考察、开挖探槽、 GPS地形剖面测量及OSL测年等开展了相关研究, 结果表明: 柴达木盆地北缘断裂锡铁山段的遥感影像线性特征明显, 存在一系列断层陡坎、断层三角面、水系扭错等地貌现象, 是一条以走滑为主、逆冲为辅的全新世活动断裂。综合分析锡铁山镇西和全集河东2处不同期次洪积扇的垂直位错以及相应地貌面的年龄, 并通过实测该区地貌面的水平、垂直位错数据, 得到该断裂全新世晚期(3.2ka BP)以来的水平滑动速率为1.81~2.1mm/a, 平均逆冲速率为0.33~0.38mm/a。

关键词: 柴达木盆地北缘断裂, 锡铁山, 左旋走滑, 走滑断裂, 逆冲断裂, 活动速率

CLC Number:

P315.2

YAO Sheng-hai, GAI Hai-long, YIN Xiang, LIU Wei, ZHANG Jia-qing, YUAN Jian-xin. TECTONIC GEOMORPHOLOGY AND QUATERNARY SLIP RATE OF THE XITIESHAN SECTION OF THE NORTHERN MARGIN FAULT OF QAIDAM BASIN[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(6): 1385-1400.

姚生海, 盖海龙, 殷翔, 刘炜, 张加庆, 袁建新. 柴达木盆地北缘断裂(锡铁山段)的构造地貌特征与晚第四纪活动速率[J]. 地震地质, 2020, 42(6): 1385-1400.

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